1. Field of the Invention
The present invention relates to a process for producing L-cysteine or a derivative thereof in the presence of cysteine desulfhydrase which is derived mainly from microorganisms.
2. Description of the Prior Art
L-Cysteine is a quasi-essential amino acid which is useful as a food additive and a pharmaceutical, e.g., as an antidote. In addition, L-cysteine is useful as an intermediate in the preparation of other pharmaceutical compounds. The derivatives of L-cysteine, for example, the sulfoxides of S-methyl-L-cysteine and S-allyl-L-cysteine, are known to suppress increasing levels of cholesterol in blood and liver.
The known processes for the production of cysteine include: (1) extraction of cystine from a hydrolysate of natural products such as man's hair, followed by reduction of cystine; (2) condensation of benzyl chloromethyl sulfide with diethyl phthalimidomalonate, followed by hydrolysis and reduction; (3) hydrolysis of the thiazoline derivative obtained by the reaction of N-thiobenzoylserine with thionyl chloride; and (4) enzymatic processes. Among these processes, organic synthesis are unfavorable because of high production costs due to the complicated nature of the reactions and the racemic resolutions required to obtain L-cysteine.
The known enzymatic processes include: (1) synthesis of L-cysteine from serine and hydrogen sulfide in the presence of cysteine synthetase derived from Neurospora crassa (OLS 2,225,797; J. Biol. Chem., 242, 12 (1967)); (2) synthesis of L-cysteine from serine and hydrogen sulfide in the presence of serine sulfhydrase (Biochemische Zeitschrift 336, 258-273 (1962)); (3) synthesis of L-cysteine from .beta.-chloroalanine and hydrogen sulfide in the presence of serine sulfhydrase. (Proceedings of the Joint U.s.-U.S.S.R. Symposium on Biological Pyridoxal Catalysis; Leningrad, U.S.S.R. (August 16-23, 1974) P.155); and (4) synthesis of L-cysteine from methionine and serine in the presence of dandruff of animals. (Japanese Pat. published No. 16019/1962, Chemical Abstracts 57 5150i). These enzymatic processes, however, are not always suitable for industrial production of L-cysteine. Consequently, it would be most desirable to have a new enzymatic process free of this defect.